Vibratory flow meter with multichannel flow tube

ABSTRACT

Vibratory meters ( 5 ), and methods for their use measuring a fluid are provided. Each vibratory meter includes a multichannel flow tube ( 300 ) comprising two or more fluid channels ( 302 ), a pickoff ( 170 ), a driver ( 180 ), and meter electronics ( 20 ) configured to apply a drive signal to the driver at a drive frequency ω, and measure a deflection of the multichannel flow tube with the pickoff. In examples, at least one fluid channel has an effective diameter that is related to velocity of sound and drive velocity. In further examples, the driver may apply a drive signal to the driver having a drive frequency proportional to the velocity of sound and effective diameter.

CROSS-REFERENCE TO RELATED APPLICATION

This is a Continuation Application of and claims priority fromInternational Application No. PCT/US2017/048139, filed Aug. 23, 2017,entitled “VIBRATORY FLOW METER WITH MULTICHANNEL FLOW TUBE,” thecontents of which are incorporated herein by reference.

TECHNICAL FIELD

The examples described below relate to vibratory meters and methods forusing vibratory meters. More particularly, the examples are directed tovibratory meters including multichannel flow tubes.

TECHNICAL FIELD

Vibratory meters, such as Coriolis mass flowmeters and vibratingdensitometers, typically operate by detecting motion of a vibrating flowtube that contains a flowing material. Properties associated with thematerial in the flow tube, such as mass flow, density and the like, canbe determined by processing measurement signals received from motiontransducers associated with the flow tube. Vibratory meters have meterassemblies with one or more flow tubes of a straight or curvedconfiguration. Each flow tube configuration in a Coriolis mass flowmeter, for example, has a set of natural vibration modes, which may beof simple bending, torsional, or coupled type. Each flow tube can bedriven to oscillate at a preferred mode. When there is no flow throughthe flowmeter, a driving force applied to the flow tube(s) causes allpoints along the flow tube(s) to oscillate with identical phase or witha small “zero offset”, which is a time delay measured at zero flow.

As material begins to flow through the flow tube(s), Coriolis forcescause each point along the flow tube(s) to have a different phase. Forexample, the phase at the inlet end of the flowmeter lags the phase atthe centralized driver position, while the phase at the outlet leads thephase at the centralized driver position. Pickoffs on the flow tube(s)produce sinusoidal signals representative of the motion of the flowtube(s). Signals output from the pickoffs are processed to determine thetime delay between the pickoffs. The time delay between the two or morepickoffs is proportional to the mass flow rate of material flowingthrough the flow tube(s).

A meter electronics connected to the driver generates a drive signal tooperate the driver, and to determine a mass flow rate and/or otherproperties of a process material from signals received from thepickoffs. The driver may comprise one of many well-known arrangements;however, a magnet and an opposing drive coil have received great successin the flowmeter industry. An alternating current is passed to the drivecoil for vibrating the flow tube(s) at a desired flow tube amplitude andfrequency. It is also known in the art to provide the pickoffs as amagnet and coil arrangement very similar to the driver arrangement.

Entrained gas in liquid and wet gases are common application problemsfor Coriolis flow meters, especially in the oil and gas productionindustry. The particles, or gas bubbles/liquid droplets that form insideof a bulk fluid can decouple from the bulk fluid when the vibratorymeter is vibrated. Additionally, velocity of sound (VOS) effects foundin multiphase fluids and single phase gases can cause furthermeasurement errors. Flow profile effects are another area of concern forall types of flow meters. When a Reynolds number is low, typically dueto high viscosity of a fluid in the flow meter, there areviscosity-related effects, which can reduce the sensitivity of a flowmeter. Larger meters, which have a smaller tube length to tube diameterratio, can be more adversely affected.

Prior solutions to the challenges of measuring multiphase fluids haveincorporated ways to identify and/or filter out decoupling errors frommeasurements, and have included: alarm handling, signal processing andnoise rejection, and wider mode separation into vibratory meters. Whilethe prior solutions have provided some improvements, meter performancehas continued to be impacted by decoupling errors.

Prior solutions to the challenges of VOS effects have included measuringthe speed of sound and the pressure of the process fluid to estimate themeasurement errors caused. Other methods including user entry of fluiddata have also been proposed. Including additional sensors and detectorswith a flowmeter adds complexity to a flowmeter, however, which isundesirable, and fluid property data entered by users can be enteredincorrectly, or can vary over time.

Prior solutions to the challenges of flow profile effects have includedproviding flow meters with relatively long flow tube lengths. While thissolution has provided a flow meter with fewer measurement errors, thelarger flow meter dimensions that result are not appropriate for manyprocess applications.

Accordingly, there is a need for flow tubes and flow meters that canaccurately measure a flow rate of a fluid in view of multiphase,decoupling, VOS, or flow profile effects by removing the source of theerrors themselves. Such solutions can be realized with a multichannelflow tube.

SUMMARY

A method of measuring a fluid with a vibratory flow meter including amultichannel flow tube is provided. The method comprises flowing thefluid into two or more fluid channels in the multichannel flow tube, thetwo or more channels formed by a tube perimeter wall and one or morechannel divisions extending along at least a portion of the tubeperimeter wall, applying a drive signal to a driver coupled to themultichannel flow tube, the driver being configured to vibrate themultichannel flow tube in response to the drive signal, and measuring adeflection of the multichannel flow tube with a pickoff attached to themultichannel flow tube, wherein the fluid has a velocity of sound c andan effective diameter d_(eff) of at least one of the two or more fluidchannels is:

$d_{eff} \leq {0.0894{\frac{c}{\omega}.}}$

A method of measuring a fluid with a vibratory meter comprising amultichannel flow tube is provided. The method comprises receiving avelocity of sound c for the fluid, receiving an effective diameterd_(eff) of at least one of the two or more fluid channels of themultichannel flow tube, the two or more channels formed by a tubeperimeter wall and one or more channel divisions extending along atleast a portion of the tube perimeter wall, determining a drivefrequency ω, wherein

${\omega \leq {0.0894\frac{c}{d_{eff}}}},$

applying a drive signal at the drive frequency ω to a driver coupled tothe multichannel flow tube, and measuring a deflection of themultichannel flow tube with a pickoff attached to the multichannel flowtube.

A vibratory meter (5) including a multichannel flow tube (300, 400, 500)is provided. The vibratory meter comprises a meter assembly (10)communicatively coupled to a meter electronics (20). The meter assemblycomprises the multichannel flow tube comprising two or more fluidchannels (302, 402, 502) formed by a tube perimeter wall (304, 404, 504)and one or more channel divisions (306, 406, 506) extending along atleast a portion of the tube perimeter wall, at least one of the two ormore fluid channels having an effective diameter d_(eff) (1114), apickoff (170 l, 170 r) attached to the multichannel flow tube, a driver(180) coupled to the multichannel flow tube, the driver being configuredto vibrate the multichannel flow tube. The meter electronics is coupledto the driver, with the meter electronics being configured to receive aninverse Stokes number δ(1112) and a kinematic viscosity ν(1110) for thefluid, receive the effective diameter (114) d_(eff) for at least one ofthe two or more fluid channels of the multichannel flow tube, determinea drive frequency ω (1108), wherein the fluid has a velocity of sound c(1118), and the drive frequency ω is:

${\omega \leq {0.0894\; \frac{c}{d_{eff}}}},$

apply a drive signal at the drive frequency ω to the driver coupled tothe multichannel flow tube, and measure a deflection of the multichannelflow tube with the pickoff attached to the multichannel flow tube.

ASPECTS

According to a further aspect, the fluid may be a multiphase fluid.

According to a further aspect, each of the two or more fluid channelsmay have the effective diameter d_(eff) in at least a first dimension.

According to a further aspect, at least one of the two or more fluidchannels may have an effective diameter d_(eff) in a first dimension anda second dimension.

According to a further aspect, the effective diameter d_(eff) of the twoor more fluid channels may be less than 0.3 inches.

According to a further aspect, the tube perimeter wall of themultichannel flow tube may be substantially circular.

According to a further aspect, the one or more channel divisions may besubstantially straight.

According to a further aspect, the one or more channel divisions may besubstantially circular.

According to a further aspect, each of the two or more fluid channelsmay have the effective diameter d_(eff) in a first dimension.

According to a further aspect, at least one of the two or more fluidchannels may have an effective diameter d_(eff) in a first dimension anda second dimension.

According to a further aspect, the one or more channel divisions may besubstantially straight.

According to a further aspect, the one or more channel divisions may besubstantially circular.

According to a further aspect, the effective diameter d_(eff) of the twoor more fluid channels may be less than 0.3 inches.

BRIEF DESCRIPTION OF THE DRAWINGS

The same reference number represents the same element on all drawings.The drawings are not necessarily to scale.

FIG. 1 depicts a vibratory flowmeter, in accordance with an example;

FIG. 2 depicts a cross-section of a flow tube of a vibratory flowmeter;

FIG. 3 depicts a cross-section of a multichannel flow tube, inaccordance with an example;

FIG. 4 depicts a cross-section of a multichannel flow tube, inaccordance with an example;

FIG. 5 depicts a cross-section of a multichannel flow tube, inaccordance with an example;

FIG. 6 depicts a method, in accordance with an example;

FIG. 7 depicts a method, in accordance with an example;

FIG. 8 depicts a method, in accordance with an example;

FIG. 9 depicts a method, in accordance with an example;

FIG. 10 depicts a method, in accordance with an example; and

FIG. 11 depicts a meter electronics, in accordance with an example.

DETAILED DESCRIPTION

The present disclosure describes vibratory meters including multichannelflow tubes, and methods of measuring a fluid with a vibratory flow meterincluding a multichannel flow tube.

FIG. 1 depicts a vibratory meter 5 with a multichannel flow tube 130 inaccordance with an example. As shown in FIG. 1, the vibratory meter 5comprises a meter assembly 10 and meter electronics 20. The meterassembly 10 responds to the mass flow rate and density of a processmaterial. The meter electronics 20 is connected to the meter assembly 10via leads 100 to provide density, mass flow rate, and temperatureinformation over communications path 26, as well as other information.Information and commands may be further received at meter electronics 20over communications path 26.

A Coriolis flow meter structure is described, although this is notintended to be limiting. Those of skill will readily understand that thepresent Application could be practiced as a vibrating tube densitometer,tuning fork densitometer, or the like.

The meter assembly 10 includes a pair of manifolds 150 and 150′, flanges103 and 103′ having flange necks 110 and 110′, a pair of parallelmultichannel flow tubes 130 and 130′, driver 180, and a pair of pick-offsensors 170 l and 170 r. Multichannel flow tubes 130 and 130′ have twoessentially straight inlet legs 131, 131′ and outlet legs 133, 133′,which converge towards each other at flow tube mounting blocks 120 and120′. The multichannel flow tubes 130, 130′ bend at two symmetricallocations along their length and are essentially parallel throughouttheir length. Brace bars 140 and 140′ serve to define the axis W and W′about which each multichannel flow tube 130, 130′ oscillates. The legs131, 131′ and 133, 133′ of the multichannel flow tubes 130, 130′ arefixedly attached to flow tube mounting blocks 120 and 120′ and theseblocks, in turn, are fixedly attached to manifolds 150 and 150′. Thisprovides a continuous closed material path through meter assembly 10.

When flanges 103 and 103′, having holes 102 and 102′ are connected, viainlet end 104 and outlet end 104′ into a process line (not shown) whichcarries the process material that is being measured, material entersinlet end 104 of the meter through an orifice 101 in the flange 103 andis conducted through the manifold 150 to the flow tube mounting block120 having a surface 121. Within the manifold 150, the material isdivided and routed through the multichannel flow tubes 130, 130′. Uponexiting the multichannel flow tubes 130, 130′, the process material isrecombined in a single stream within the flow tube mounting block 120′having a surface 121′ and the manifold 150′ and is thereafter routed tooutlet end 104′ connected by the flange 103′ having holes 102′ to theprocess line (not shown).

The multichannel flow tubes 130, 130′ are selected and appropriatelymounted to the flow tube mounting blocks 120, 120′ to have substantiallythe same mass distribution, moments of inertia and Young's modulus aboutbending axes W-W and W′-W′, respectively. These bending axes go throughthe brace bars 140, 140′.

Both multichannel flow tubes 130, 130′ are driven by driver 180 inopposite directions about their respective bending axes W and W′ and atwhat is termed the first out-of-phase bending mode of the flow meter.This driver 180 may comprise any one of many well-known arrangements,such as a magnet mounted to the multichannel flow tube 130′ and anopposing coil mounted to the multichannel flow tube 130 and throughwhich an alternating current is passed for vibrating both multichannelflow tubes 130, 130′. A suitable drive signal is applied by the meterelectronics 20, via lead 185, to the driver 180.

The meter electronics 20 receives the left and right sensor signalsappearing on leads 165 l, 165 r, respectively. The meter electronics 20produces the drive signal appearing on lead 185 to driver 180 andvibrate multichannel flow tubes 130, 130′. The meter electronics 20processes the left and right sensor signals and the RTD signal tocompute the mass flow rate and the density of the material passingthrough meter assembly 10. This information, along with otherinformation, may be transmitted by meter electronics 20 overcommunications path 26.

While FIG. 1 depicts a single meter assembly 10 in communication withmeter electronics 20, those skilled in the art will readily appreciatethat multiple sensor assemblies may be in communication with meterelectronics 20. Further, meter electronics 20 may be capable ofoperating a variety of different sensor types. Each sensor assembly,such as the meter assembly 10 in communication with meter electronics20, may have a dedicated section of a storage system within meterelectronics 20.

Meter electronics 20 may include various other components and functions,as will be understood by those of skill. These additional features maybe omitted from the description and the figures for brevity and clarity.

Vibratory meter 5 includes multichannel flow tubes 130, 130′.Multichannel flow tubes 130, 130′ have a plurality of fluid channelsthrough which a material, such as a single phase or multiphase fluid,can flow. That is, the fluid flowing through the multichannel flow tubes130, 130′ may flow through two or more fluid channels. The multichannelflow tubes 130, 130′ may improve errors in multiphase measurement byaddressing issues associated with fluid decoupling, VOS errors, or flowprofile effects.

FIG. 2 depicts a flow tube 200. Flow tube 200 includes a tube perimeterwall 202. A decoupling error may be caused in a vibratory flow meterincluding flow tube 200 when a multiphase fluid having a bulk fluid, forexample a liquid or gas, includes particles, for example liquiddroplets, solids, or gas bubbles, having a density that is differentfrom the bulk fluid. The decoupling of particles within the multiphasefluid during the vibration of the flow tube 200 provides a source oferror in vibratory meter measurements.

When flow tube 200 is oscillated with a multiphase fluid, thedistribution of particles within the bulk fluid may not represent auniform distribution of particles in an infinite liquid medium. Also,wall effects can prevent decoupling of particles in a bulk fluid fromoccurring in areas near to tube perimeter wall 202. It has been showncomputationally that wall effects are negligible unless a particle iswithin a distance of two particle radii from the wall. (Fischer PF etal. 2005. Influence of wall proximity on the lift and drag of a particlein an oscillatory flow. J. Fluids Eng. 127:583-595). For a tube diameterof d_(eff) and a particle radius r_(part), the following relationshiptherefore describes when wall effects prevent particle decoupling:

d_(eff)≤6r_(part).  (Equation 1)

Although tube perimeter wall 202 is depicted in FIG. 2 as being ofnegligible thickness, tube diameter d_(eff) references the innerdiameter within a flow tube, through which fluid may be free to flow.

FIG. 2 depicts this relationship schematically with example particle204. Particle 204 is constrained from decoupling due to wall effectsbecause the effective diameter d_(eff) 208 of flow tube 200 is equal to6r_(part).

For many vibratory meters, however, multiphase fluid particles would besmall compared to the tube diameter, and wall effects are negligible.This provides for decoupling and large measurement errors.

It is possible to use the inverse Stokes number as a measure of particledecoupling. The inverse Stokes number δ, represents a ratio of theoscillation time scale to the viscous diffusion time scale. Thisparameter can provide an extremely important way to predict the motionof an oscillating particle. The inverse Stokes number relates kinematicviscosity ν, frequency ω, and particle radius r_(part):

$\begin{matrix}{\delta = \sqrt{\frac{2\; v}{\omega \; r_{part}^{2}}}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

When the inverse Stokes number δ for a multiphase fluid is large, theamplitude of decoupling is low. Low inverse Stokes numbers maycorrespond to high amounts of decoupling when the kinematic viscosity ofa fluid is low, the particle size is high, or the meter vibrationfrequency ω is high. By combining Equations 1 and 2, it is possible toexpress d_(eff) in terms of the inverse Stokes number δ:

$\begin{matrix}{d_{eff} \leq {6{\sqrt{\frac{2v}{{\omega\delta}^{2}}}.}}} & \left( {{Equation}\mspace{14mu} 3} \right)\end{matrix}$

As may be seen from Equation 3, a very high frequency meter may benefitfrom a smaller effective diameter to prevent decoupling at a givenparticle size. Because the inverse Stokes number δ may account for arange of drive frequency ω values and particle radii r_(part) values,Equation 3 may be used to create a vibratory meter configured to measurea wide range of multiphase fluids.

In examples, d_(eff) may be less than 0.3 inches. In further examples,d_(eff) may be between 0.25 and 0.3 inches. In further examples,however, d_(eff) may be any other value that may provide wall effectsbenefits described above, as will be understood by those of skill.

In examples, particle radius r_(part) may represent a distribution ofparticle sizes that are related to surface tension, turbulence (flowrate), or other factors of the multiphase fluid. In further examples,particle radius r_(part) may represent a mean or a median of adistribution of particle sizes.

By solving Equation 3 for drive frequency ω, it may be possible todetermine a drive frequency ω to operate a vibratory meter that willminimize decoupling for a multiphase fluid with a known kinematicviscosity ν, inverse stokes number δ, and a multichannel flow tube witha known effective diameter d_(eff′):

$\begin{matrix}{\omega \leq {\frac{72v}{\delta^{2}d_{eff}^{2}}.}} & \left( {{Equation}\mspace{14mu} 4} \right)\end{matrix}$

In examples, frequency ω may be 100 Hz or less.

In addition to the decoupling errors caused by the relative motion ofbubbles and particles in a multiphase fluid, Coriolis meters may alsoexperience velocity of sound effects when the sonic velocity of themeasurement fluid is low, or the oscillation frequency ω of the meter ishigh. Gases have lower sonic velocities than liquids, and low velocitiesmay result from a mixture of the two. The addition of even a smallamount of gas to a liquid may result in a dramatic reduction in thevelocity of sound of the multiphase fluid below that of eitherindependent phase.

The oscillation of a flow tube may produce sound waves that oscillate inthe transverse direction at the drive frequency of the meter. When thevelocity of sound of the fluid is high, as it may be for a single-phaseliquid, the first acoustic mode for transverse sound waves across thecircular conduit may be at a much higher frequency than the drivefrequency. However, when the velocity of sound drops, due for example,to the addition of gas to a liquid, the frequency of the acoustic modealso drops. When the frequency of the acoustic mode and the drive modeare close, meter errors result due to the off-resonance excitation ofthe acoustic mode by the drive mode. For small diameter or low frequencymeters at typical process pressures, velocity of sound effects can benegligible with respect to the specified accuracy of the meter. However,for large diameter or high frequency Coriolis meters, the velocity ofsound can be low enough to cause significant measurement errors due tointeraction between the drive and fluid vibration modes.

As described by Hemp and Kutin in 2006 (J. HEMP AND J. KUTIN. 2006.Theory of errors in Coriolis flowmeter readings due to compressibilityof the fluid being metered. Flow Measurement and Instrumentation.17:359-369.), in applications where velocity of sound effects (VOS) maybe a concern, the following equation predicts the mass flow error {dotover (m)}_(VOS,err), expressed as a percentage of flow error:

$\begin{matrix}{{{\overset{.}{m}}_{{VOS},{err}} = {\frac{1}{2}\left( \frac{\omega \; d_{eff}}{2c} \right)^{2} \times 100}},} & \left( {{Equation}\mspace{14mu} 5} \right)\end{matrix}$

where c is the speed of sound in the fluid, and ω is the drive frequencyof the flow tube. For an error threshold {dot over (m)}_(VOS,err) of0.1% of mass flow {dot over (m)}, the following constraint may beestablished:

$\begin{matrix}{d_{eff} \leq {0.0894\; {\frac{c}{\omega}.}}} & \left( {{Equation}\mspace{14mu} 6} \right)\end{matrix}$

For example, when ambient air, with a speed of sound c of 13,504 in/s,is measured with a flow meter operating at a drive frequency 300 Hz,resulting in an angular velocity of 2*π*300=1,885 rad/s, with amultichannel flow tube with an effective diameter d_(eff) that is lessthan 0.640 inches, a 0.1% error threshold {dot over (m)}_(VOS,err) maybe achieved. In other applications, including single phase andmultiphase fluids, flow profile effects can be a concern. The ratio ofthe length (L) of the flow tube to its diameter (D), or inner diameter,is an important meter consideration when flow profile effects are atissue. Larger vibratory meters tend to have relatively low L/D ratios.Extensive laboratory experimentation has shown that flow meters with L/Dratios that are 25 or above have fewer flow profile effects. For a tubebundle meter, the effective diameter d_(eff) may therefore be selectedto meet the following constraint:

$\begin{matrix}{d_{eff} \leq \frac{L}{25}} & \left( {{Equation}\mspace{14mu} 7} \right)\end{matrix}$

For example, a flow meter with an active flow tube length L of 75 incheswould have reduced flow effects if effective diameter d_(eff) was lessthan 3 inches. For a flow tube with a flow tube perimeter having adiameter of 4.5 inches, a single baffle may eliminate the LD effect.

Multi-channel flow tubes with effective diameters d_(eff) determinedaccording to the equations provided above may improve the accuracy ofvibratory meter measurement by addressing issues associated with fluiddecoupling, velocity of sound (VOS) effects, and flow effects. Themulti-channel flow tubes 300, 400, 500 described below may help reducethese error mechanisms from occurring in the first instance, instead ofremoving these errors in post processing, as taught by the prior art.The multi-channel flow tubes 300, 400, 500 may also reduce the flowprofile effects by effectively increasing the tube length (L) to tubediameter (D) ratio without increasing the size of the flow meter, as isexplained in more detail below.

FIG. 3 depicts a cross-section of example multichannel flow tube 300,according to an example. A reference coordinate system with x and y-axesis depicted on each of FIGS. 3-5 for clarity. Multichannel flow tube 300comprises two or more fluid channels 302 formed by a tube perimeter wall304 and one or more channel divisions 306. In the example ofmultichannel flow tube 300, the tube perimeter wall 304 is substantiallycircular in shape. In some examples, substantially circular may meanmore than 50% of tube perimeter wall 304 is circular in shape. Infurther examples, substantially circular may mean more than 75% of tubeperimeter wall 304 is circular in shape. In further examples, however,tube perimeter wall 304 may be any other shape, as will be understood bythose of skill. In example multichannel flow tube 300, the one or morechannel divisions 306 are substantially straight walls that are arrangedto be parallel with one another. The channel divisions 306 are coupledto tube perimeter wall 304 at their ends.

The areas between the interior surface of tube perimeter wall 304 andthe channel divisions 306 define one or more fluid channels 302, throughwhich fluid may flow within the multichannel flow tube. At least one ofone or more fluid channels 302 may have an effective diameter d_(eff)308, or the distance at the widest point between adjacent sections oftube perimeter wall 304 and/or channel divisions 306, in a firstdirection. For example, one or more of fluid channels 302 may have aneffective diameter d_(eff) in the x direction. In examples, the xdirection may be the direction in which multichannel flow tube 300 isprimarily oscillated. In further examples, however, the x direction maybe different from the direction in which multichannel flow tube 300 isprimarily oscillated. Effective diameter d_(eff) 308 may therefore helpprevent decoupling of particles from a multiphase fluid in the drivedirection.

FIG. 4 depicts a cross-section of multichannel flow tube 400, inaccordance with an example. Multichannel flow tube 400 comprises two ormore fluid channels 402 formed by a tube perimeter wall 404 and one ormore channel divisions 406 a, 406 b. In the example of multichannel flowtube 400, the tube perimeter wall 404 is substantially circular inshape.

Like multichannel flow tube 300, multichannel flow tube 400 includes afirst set of channel divisions 406 a that are substantially straightwalls, arranged in a substantially parallel configuration with oneanother, and coupled to tube perimeter wall 404 at their respectiveends. Multichannel flow tube 400 further includes a second set ofchannel divisions 406 b that are arranged to be perpendicular to thefirst set of channel divisions 406 a, however.

Some of fluid channels 402 are therefore formed between adjacent tubeperimeter wall 404, channel divisions 406 a, and channel divisions 406b, and some of fluid channels 402 are formed between adjacent channeldivisions 406 a and 406 b. At least one fluid channel 402 may have aneffective diameter d_(eff) 408 a, or the distance at the widest pointbetween adjacent sections of tube perimeter wall 404 and/or opposingchannel divisions 406 a or 406 b, in a first direction. For example, oneor more of fluid channels 402 may have an effective diameter d_(eff) 408a in the x direction. At least one of one or more fluid channels 402 mayfurther have an effective diameter d_(eff), in a second direction. Forexample, one or more fluid channels 402 may further have an effectivediameter d_(eff) 408 b in the y direction. By including one or morefluid channels with effective diameter d_(eff) 408 a in the firstdirection and effective diameter d_(eff) 408 b in the second direction,it may be possible to prevent decoupling of particles from a multiphasefluid in a vibratory meter when driving a multichannel tube will includedisplacement in more than one direction, for example when a flow tubewill twist or rotate around an axis such as axis W or W′.

FIG. 5 depicts a cross-section of a further multichannel flow tube 500,in accordance with an example. Multichannel flow tube 500 comprises atube perimeter wall 504, and two or more fluid channels 502. Fluidchannels 502 are formed by one or more channel divisions 506. Channeldivisions 506 are substantially circular in shape.

In the example of multichannel flow tube 500, effective diameter d_(eff)508 is the diameter of each respective channel division 506. Because theeffective diameter d_(eff) 508 is substantially the same in everydirection within the plane of the cross section, multichannel flow tube500 may help prevent decoupling of particles from a multiphase fluid inany direction.

The examples of multichannel flow tubes 300, 400, and 500 are notintended to be limiting. As will be understood by those of skill, infurther examples, multichannel flow tubes may include differentconfigurations of tube perimeter wall. In further examples, multichannelflow tubes may include any number or orientation of channel divisionsthat allow for the formation of an effective diameter d_(eff) in atleast one dimension according to Equations 3, 6 or 7.

In examples, multichannel flow tubes 300, 400, or 500 may includechannel divisions 306, 406, or 506 along the entire length of the flowtube. In other examples, the channel divisions may only extend along thevibrating region of the flow tube. In further examples, however, thechannel divisions may only extend along a portion of the vibratingregion of the multichannel flow tube, to balance the error reducingeffects of the fluid channels with the potential pressure drop that theymay cause in the multichannel flow tube 300, 400, or 500.

A multi-channel flow tube 300, 400, 500 may reduce or eliminate theseproblems relating to multiphase decoupling, VOS, or flow effects becausethe effective tube diameter, d_(eff), may be considerably less than astandard flow tube. Advantageously, prior flow meters may be retrofittedwith multichannel flow tubes having the d_(eff) described in any ofEquations 3, 6 or 7 to gain the advantages provided by a smaller flowtube effective diameter d_(eff).

Because multichannel flow tubes 300, 400, 500 have a lower effectivediameter d_(eff), they may be used to increase the L/D ratios of higherflow rate vibratory meters to eliminate flow profile effect in largervibratory meters. In fact, a multi-channel flow tube with individualtube diameters even one half as large as the tube perimeter wall 302,402, or 502 would result in L/D ratios above 25 for vibratory meters ofmany common sizes. Additionally, multichannel flow tubes can be used toallow for a more compact Coriolis meter in any line size that does notsuffer from flow profile effects.

FIG. 11 depicts meter electronics 20 of the vibratory meter 5 accordingto an example of the Application. Meter electronics 20 may include aninterface 1101 and a processing system 1103. The processing system 1103may include a storage system 1104. As previously discussed, meterelectronics 20 may generate a drive signal to supply to driver 180 andreceive signals from pickoff sensor(s) 170 l, 170 r. Meter electronics20 may operate meter assembly 10 as a density meter, a viscosity meter,or a flow meter such as a Coriolis mass flow meter. It should beappreciated that meter electronics 20 may also operate other types ofvibrating meters, and the examples provided should not limit the scopeof the present invention. Meter electronics 20 may process vibratorysensor signals to obtain one or more characteristics of the fluidpassing through multichannel flow tube(s) 130, 130′.

Interface 1101 may receive sensor signals from the driver 180, orpickoff(s) 170 l, 170 r, via leads 100. Interface 1101 may perform anynecessary or desired signal conditioning, such as any manner offormatting, amplification, buffering, etc. Alternatively, some or allthe signal conditioning may be performed in processing system 1103. Inaddition, interface 1101 may enable communications between meterelectronics 20 and external devices. In addition, interface 1101 mayenable communications between meter electronics 20 and external devices,for example. Interface 1101 may be capable of any manner of electronic,optical, or wireless communication.

Interface 1101 in one example may include a digitizer (not shown),wherein meter assembly 10 signals comprise analog sensor signals. Thedigitizer may sample and digitize the analog sensor signals and producedigital sensor signals. The digitizer may also perform any neededdecimation, wherein the digital sensor signal is decimated to reduce theamount of signal processing needed and to reduce the processing time.

Processing system 1103 conducts operations of meter electronics 20 andprocesses density/viscosity/flow measurements from meter assembly 10.Processing system 1103 may also execute one or more processing routinessuch as vibratory meter measurement routine 1106 and/or drive frequencydetermination routine 1116.

Processing system 1103 may comprise a general purpose computer, amicro-processing system, a logic circuit, or any other general purposeor customized processing device capable of performing the functionsdescribed herein. Processing system 1103 may be distributed amongmultiple processing devices. Processing system 1103 may include anymanner of integral or independent electronic storage medium, such asstorage system 1104.

Storage system 1104 may store meter parameters and data, softwareroutines, constant values, and variable values. Storage system 1104 maycomprise a primary or main memory, such as a random access memory (RAM).In examples, storage system 1104 may include a hard disk drive, aremovable storage device, a memory card, a floppy disk drive, a magnetictape drive, a compact disk drive, a digital versatile disc, a Blue-raydisc, an optical storage device, tape backup, or any other computeruseable or readable storage medium. In examples, storage system 1104 maycomprise a non-transitory media.

Storage system 1104 may further store variables that may be used byvibratory meter measurement routine 1106 and/or drive a drive frequencydetermination routine 1116. For example, storage system 1104 stores adrive frequency ω 1108, a kinematic viscosity ν 1110, a Stokes number δ1112, an effective diameter d_(eff) 1114, velocity of sound c 1118, orflow tube length L, as described above.

In an example, the storage system 1104 includes routines that areexecuted by the processing system 1103. For example, the storage system1104 may store vibratory meter measurement routine 1106 and/or drivefrequency determination routine 1116. Meter electronics 20 may initiatevibratory meter measurement routine 1106 to take a measurement of afluid using meter assembly 10. In examples, vibratory meter measurementroutine 1106 may determine mass flow, density, or viscosity of a processfluid, as described above. Meter electronics 20 may further initiatedrive frequency determination routine 1116. In examples, drive frequencydetermination routine 1116 may be used to determine a drive frequency ω1108 used to operate the vibratory meter 5 using vibratory metermeasurement routine 1106.

FIGS. 6, 7, 8, 9, and 10 depict methods 600, 700, 800, 900, and 1000respectively. Steps 604 and 606 of method 600, steps 708 and 710 ofmethod 700, steps 804 and 806 of method 800, steps 908 and 910 of method900, and steps 1004 and 1006 of method 1000 each comprise examples ofvibratory meter measurement routine 1106. Steps 702, 704, and 706 ofmethod 700, and steps 902, 904, and 906 of method 900 comprise anexample of drive frequency determination routine 1116. Processing system1103 may be configured to perform the necessary signal and dataprocessing to execute vibratory meter measurement routine 1106 and/ordrive frequency determination routine 1116, which may include performingany combination of sensor verification methods 600, 700, 800, 900, or1000.

FIG. 6 depicts method 600, in accordance with an example. Method 600 maybe executed to measure a fluid with a vibratory flow meter including amultichannel flow tube. Method 600 begins with step 602. In step 602,fluid is flowed into two or more fluid channels in the multichannel flowtube, the two or more channels formed by a tube perimeter wall and oneor more channel divisions extending along at least a portion of the tubeperimeter wall.

For example, fluid may flow into two or more fluid channels 302, 402,502 in multichannel flow tube 300, 400, 500 formed by tube perimeterwall 304, 404, 504 and one or more channel divisions 306, 406, 506.

Method 600 continues with step 604. In step 604, a drive signal isapplied to a driver coupled to the multichannel flow tube, the driverbeing configured to vibrate the multichannel flow tube at a drivefrequency win response to the drive signal.

For example, a drive signal may be applied from meter electronics 20over lead 185 to driver 180. Driver 180 may cause multichannel flowtubes 300, 400, 500 to vibrate at drive frequency ω in response to thedrive signal.

Method 600 continues with step 606. In step 606, a deflection of themultichannel flow tube is measured with a pickoff attached to themultichannel flow tube, wherein the fluid has a kinematic viscosity vand an inverse Stokes number δ and an effective diameter d_(eff) of atleast one of the two or more fluid channels is

$d_{eff} \leq {6{\sqrt{\frac{2v}{\omega \; \delta^{2}}}.}}$

For example, a deflection of multichannel flow tubes 300, 400, 500 maybe measured with pickoff 170 l and/or 170 r attached to the multichannelflow tube. The at least one of the two or more fluid channels 302, 402,502 include effective diameter d_(eff) 308, 408, 508, which may bedetermined as described in Equation 3.

Method 600 may provide for improved accuracy in measuring by preventingparticle decoupling in a greater range of multiphase fluids, including avariety of bulk fluids and particle sizes.

FIG. 7 depicts method 700, in accordance with an example. Method 700 maybe applied to measure a fluid with a vibratory meter comprising amultichannel flow tube.

Method 700 begins with step 702. In step 702, kinematic viscosity ν 1110and/or inverse Stokes number δ 1112 are received for the fluid.Kinematic viscosity ν 1110 and/or inverse Stokes number δ 1112 may beinput by a user and saved to storage system 1104. For example, kinematicviscosity ν 1110 and/or inverse Stokes number δ 1112 may be input at thebeginning of a measurement operation, upon installation of a sensor at acustomer site, or at any other time. In other examples, kinematicviscosity ν 1110 and/or inverse Stokes number δ 1112 may be received viaelectronic message at meter electronics 20.

Method 700 continues with step 704. In step 704, effective diameterd_(eff) 1114 is received for at least one of the two or more fluidchannels of the multichannel flow tube, the two or more channels formedby a tube perimeter wall and one or more channel divisions. In examples,effective diameter d_(eff) 1114 may be input by a user and saved tostorage system 1104. For example, effective diameter d_(eff) 1114 may beinput at the beginning of a measurement operation, upon installation ofa sensor at a customer site, upon assembly of the sensor, or at anyother time. In other examples, effective diameter d_(eff) 1114 may bereceived via electronic message at meter electronics 20.

Method 700 continues with step 704. In step 706, drive frequency ω 1108is determined, wherein drive frequency

$\omega \leq {\frac{72v}{\delta^{2}d_{eff}^{2}}.}$

For example, drive frequency ω 1108 may be calculated as described withregards to Equation 4 above.

Method 700 continues with step 708. In step 708, a drive signal isapplied to a driver coupled to the multichannel flow tube. For example,a drive signal may be applied from meter electronics 20 over lead 185 todriver 180. Driver 180 may cause multichannel flow tubes 300, 400, 500to vibrate at drive frequency ω 1108 in response to the drive signal.

Method 700 continues with step 710. In step 710, a deflection of themultichannel flow tube is measured with a pickoff attached to themultichannel flow tube. For example, a deflection of multichannel flowtubes 130 and 130′ may be measured with pickoff 170 l and/or pickoff 170r. The signal(s) from pickoff(s) 170 l and/or 170 r may be transmittedvia lead(s) 165 l and/or 165 r to meter electronics 20.

Method 700 may provide for improved accuracy in measuring by preventingdecoupling in a greater range of multiphase fluids, including a varietyof bulk fluids and particle sizes in a flow meter using a high frequencyω.

FIG. 8 depicts method 800, in accordance with an example. Method 800 maybe executed to measure a fluid with a vibratory flow meter including amultichannel flow tube.

Steps 802 and 804 are similar to steps 602 and 604, described above.Method 800 continues with step 806. In step 806, a deflection of themultichannel flow tube is measured with a pickoff attached to themultichannel flow tube, wherein the fluid has a velocity of sound c andan effective diameter d_(eff) of at least one of the two or more fluidchannels is:

$d_{eff} \leq {0.0894\; {\frac{c}{\omega}.}}$

For example, a deflection of multichannel flow tubes 300, 400, 500 maybe may be measured with pickoff and/or 170 r attached to themultichannel flow tube. At least one of the two or 170 l more fluidchannels 302, 402, 502 include effective diameter d_(eff) 308, 408, 508,which may be determined as described in Equation 4.

Method 800 may provide for improved accuracy in measuring by preventingVOS errors in a greater range of fluids and meter frequencycombinations.

FIG. 9 depicts method 900, in accordance with an example. Method 900 maybe executed to measure a fluid with a vibratory flow meter including amultichannel flow tube. Method 900 begins with step 902. In step 902, avelocity of sound c is received for a fluid. In examples, velocity ofsound c may be input by a user, saved in memory, or received via anotherinstrument such as a Coriolis mass flow meter.

Step 904 is similar to step 704, as described above with respect tomethod 700.

Method 900 continues with step 906. In step 906, a drive frequency ω isdetermined, wherein

$\omega \leq {0.0894\; {\frac{c}{d_{eff}}.}}$

For example, drive frequency ω 1108 may be calculated as described withregards to Equation 6.

Steps 908 and 910 are similar to steps 708 and 710, as described abovewith respect to method 700.

Method 900 may provide for improved accuracy in measuring by preventingVOS errors in a greater range of fluids using frequency ω.

FIG. 10 depicts method 1000, in accordance with an example. Method 1000may be executed to measure a fluid with a vibratory flow meter includinga multichannel flow tube.

Steps 1002 and 1004 are similar to steps 602 and 604, described above.Method 1000 continues with step 1006. In step 1006, a deflection of themultichannel flow tube is measured with a pickoff attached to themultichannel flow tube, wherein the multichannel flow tube has an activetube length L, and an effective diameter d_(eff) of at least one of thetwo or more fluid channels is:

$d_{eff} \leq {\frac{L}{25}.}$

Effective diameter d_(eff) is determined using Equation 7, describedabove.

Method 1000 may provide for improved accuracy in measuring by preventingflow profile effects in larger meters, and may allow for designs thatachieve further compactness while still avoiding flow profile effects.

The devices and methods disclosed herein may provide for improvedaccuracy of measurement of fluids by preventing the physical effects ofdecoupling, VOS errors, and flow profile errors in the first instance.Accordingly, the multi-channel flow tubes 300, 400, and 500 may providea similar capacity to single-channel flow tubes (i.e., flow tubeswithout the two or more fluid channels 302, 402, 502) while realizingbenefits associated with the smaller effective diameter.

The detailed descriptions of the above examples are not exhaustivedescriptions of all examples contemplated by the inventors to be withinthe scope of the Application. Indeed, persons skilled in the art willrecognize that certain elements of the above-described examples mayvariously be combined or eliminated to create further examples, and suchfurther examples fall within the scope and teachings of the Application.It will also be apparent to those of ordinary skill in the art that theabove-described examples may be combined in whole or in part to createadditional examples within the scope and teachings of the Application.Accordingly, the scope of the Application should be determined from thefollowing claims.

What is claimed is:
 1. A method of measuring a fluid with a vibratoryflow meter including a multichannel flow tube, the method comprising:flowing the fluid into two or more fluid channels in the multichannelflow tube, the two or more channels formed by a tube perimeter wall andone or more channel divisions extending along at least a portion of thetube perimeter wall; applying a drive signal to a driver coupled to themultichannel flow tube, the driver being configured to vibrate themultichannel flow tube in response to the drive signal; and measuring adeflection of the multichannel flow tube with a pickoff attached to themultichannel flow tube, wherein the fluid has a velocity of sound c andan effective diameter d_(eff) of at least one of the two or more fluidchannels is: $d_{eff} \leq {0.0894\; {\frac{c}{\omega}.}}$
 2. Themethod of claim 1, wherein the fluid is a multiphase fluid.
 3. Themethod of claim 1, wherein each of the two or more fluid channels hasthe effective diameter d_(eff) in at least a first dimension.
 4. Themethod of claim 1, wherein at least one of the two or more fluidchannels has an effective diameter d_(eff) in a first dimension and asecond dimension.
 5. The method of claim 1, wherein the effectivediameter d_(eff) of the two or more fluid channels is less than 0.3inches.
 6. The method of claim 1, wherein the one or more channeldivisions are substantially straight.
 7. The method of claim 1, whereinthe one or more channel divisions are substantially circular.
 8. Amethod of measuring a fluid with a vibratory meter comprising amultichannel flow tube, the method comprising: receiving a velocity ofsound c for the fluid; receiving an effective diameter d_(eff) of atleast one of the two or more fluid channels of the multichannel flowtube, the two or more channels formed by a tube perimeter wall and oneor more channel divisions extending along at least a portion of the tubeperimeter wall; determining a drive frequency ω, wherein${\omega \leq {0.0894\; \frac{c}{d_{eff}}}};$ applying a drive signalat the drive frequency co to a driver coupled to the multichannel flowtube; and measuring a deflection of the multichannel flow tube with apickoff attached to the multichannel flow tube.
 9. The method of claim8, wherein the fluid is a multiphase fluid.
 10. The method of claim 8,wherein each of the two or more fluid channels has the effectivediameter d_(eff) in at least a first dimension.
 11. The method of claim8, wherein at least one of the two or more fluid channels has aneffective diameter d_(eff) in a first dimension and a second dimension.12. The method of claim 8, wherein the effective diameter d_(eff) of thetwo or more fluid channels is less than 0.3 inches.
 13. The method ofclaim 8, wherein the one or more channel divisions are substantiallystraight.
 14. The method of claim 8, wherein the one or more channeldivisions are substantially circular.
 15. A vibratory meter (5)including a multichannel flow tube (300, 400, 500), the vibratory metercomprising: a meter assembly (10) communicatively coupled to a meterelectronics (20), the meter assembly comprising: the multichannel flowtube comprising two or more fluid channels (302, 402, 502) formed by atube perimeter wall (304, 404, 504) and one or more channel divisions(306, 406, 506) extending along at least a portion of the tube perimeterwall, at least one of the two or more fluid channels having an effectivediameter d_(eff) (1114), a pickoff (170 l, 170 r) attached to themultichannel flow tube, a driver (180) coupled to the multichannel flowtube, the driver being configured to vibrate the multichannel flow tube;and the meter electronics coupled to the driver, with the meterelectronics being configured to: receive an inverse Stokes number δ(1112) and a kinematic viscosity ν (1110) for the fluid; receive theeffective diameter (1114) d_(eff) for at least one of the two or morefluid channels of the multichannel flow tube; determine a drivefrequency ω (1108), wherein the fluid has a velocity of sound c (1118),and the drive frequency ω is:$\omega \leq {0.0894\; {\frac{c}{d_{eff}}.}}$ apply a drive signal atthe drive frequency ω to the driver coupled to the multichannel flowtube; and measure a deflection of the multichannel flow tube with thepickoff attached to the multichannel flow tube.
 16. The vibratory meterof claim 15, wherein each of the two or more fluid channels has theeffective diameter d_(eff) in a first dimension.
 17. The vibratory meterof claim 15, wherein at least one of the two or more fluid channels hasan effective diameter d_(eff) in a first dimension and a seconddimension.
 18. The vibratory meter of claim 15, wherein the one or morechannel divisions are substantially straight.
 19. The vibratory meter ofclaim 15, wherein the one or more channel divisions are substantiallycircular.
 20. The vibratory meter of claim 15, wherein the effectivediameter d_(eff) of the two or more fluid channels is less than 0.3inches.